Interleaved parallel inverters with integrated filter inductor and interphase transformer

ABSTRACT

A power electronics system, comprising a first inverter configured to receive DC power from a power source and a second inverter configured to receive DC power from the power source is provided. The system includes a first output inductor connected in series to an output of the first inverter, a second output inductor connected in series to an output of the second inverter, a coupling inductor configured to receive current from the first output inductor and the second output inductor, and an AC power output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/461,245, titled INTERLEAVED PARALLEL INVERTERS WITH INTEGRATED FILTERINDUCTOR AND INTERPHASE TRANSFORMER, which is a U.S. National PhaseApplication under 35 U.S.C. § 371 of International Application No.PCT/US2017/061727 titled INTERLEAVED PARALLEL INVERTERS WITH INTEGRATEDFILTER INDUCTOR AND INTERPHASE TRANSFORMER filed Nov. 15, 2017, whichclaims the benefit of an earlier filing date under 35 U.S.C. § 119(e)and claims the benefit of priority under PCT Article 8, as applicable,of U.S. Provisional Patent Application No. 62/422,838 titled COMPACT ACFILTER MODULE FOR INTERLEAVED POWER CONVERTER filed on Nov. 16, 2016,all of which are hereby incorporated by reference in their entiretiesfor all purposes.

BACKGROUND Field of Invention

Embodiments of the present invention relate generally to utility scalepower inverters.

Discussion of Related Art

A power inverter, or inverter, is an electronic device or circuitry thatconverts direct current (DC) to alternating current (AC). Inverters maybe used in a number of different contexts, with different DC powersources (such as lead acid batteries, photovoltaic solar panels, windturbines, etc), and may be designed to satisfy different power demandsof a system. Utility scale solar inverters, in particular, convertvariable DC output of a photovoltaic (PV) solar panel into a utilityfrequency AC to provide power to either a commercial electrical grid ora local, off-grid electrical network. Solar inverters are connected to aplurality of photovoltaic cells that provide DC input to the inverter.The inverter comprises at least one DC-to-AC power conversion bridge,associated filter electronics and an AC (output) module. The DC-to-ACpower conversion bridge uses a plurality of electronic switches,typically insulated gate bipolar transistors (IGBTs), and diodes toconvert the DC input into AC output. For grid-connected invertersproviding power to an electricity grid, the AC output is filtered toprovide an AC output waveform that is suitable for the grid.Furthermore, solar power inverters have special functions adapted foruse with photovoltaic arrays, including maximum power point tracking andanti-islanding protection.

A sine wave inverter produces a multiple-step sinusoidal AC waveform,although in most cases the output is a choppy or rough approximation ofa sine wave, rather than a smooth sine wave. As a substitute forstandard AC line power, power inverter devices approximate a sine waveoutput because many electrical products are engineered to work best witha sine wave AC power source. Further, grid-connected inverters aredesigned to feed power into the electric power distribution system. Theytransfer synchronously with the line, and should have as little harmoniccontent as possible.

The output from an inverter can be single phase or three-phase.Three-phase inverters are generally used in higher power applications. Abasic three-phase inverter consists of three single-phase legs eachconnected to one of the three load terminals. The operation of the threephase legs is coordinated so that one operates at each 120 degree pointof the fundamental output waveform. Certain harmonics are eliminated andother harmonics can be removed by further processing.

As shown in FIG. 1, an LC filter comprising one or more inductor andcapacitor can be used to smooth the AC waveform from a single phaseinverter (as shown in FIG. 1). Such low-pass filters allow thefundamental component of the waveform to pass to the output whilelimiting the passage of harmonic components. LC filters may similarly beused in connection with a three phase inverter, with an LC filterapplied to each output phase of the inverter.

When two or more inverters are connected in parallel, their switchingtimes (single phase or 3-phase) can be synchronized or can be offsetrelative to one another in an “interleaved” configuration. Interleavingis implemented by phase-shifting the switching times of each inverter bya unique multiple of 360°/n, where n is the number of inverters. Theswitching of the multiple inverters is thereby staggered, and theoverall switching frequency may thereby be increased.

Interleaving can result in the cancellation of higher order harmonicsand a reduction in distortion. Also, the higher frequency noise reducesthe size of the inverter AC output filters that are needed. Parallelinterleaved three-phase inverters can provide significant costreductions while improving system reliability and efficiency. FIG. 2shows two 3-phase DC-AC inverters connected in parallel, with output LCfilters.

Interleaved converters are sometimes magnetically coupled with acoupling inductor, and then share the same output filter. The couplingcombines high frequency components (which may be interleaved) and maythereby reduce ripple. FIG. 3 shows a pair of inverters (bridges)magnetically coupled via a coupling inductor which is connected to ashared LC filter. With this arrangement the combined current from bridge1 and bridge 2 passes through the output filter inductor.

SUMMARY

Particularly for large scale inverter systems, AC filters required tosmooth out the unacceptably rough AC power waveform of the inverterswould conventionally be large and costly in order to handle the level ofpower and power quality required. In accordance with principles of thepresent invention, some embodiments provide for two or more inverters tobe connected in parallel, in an extremely compact configuration, withefficient use of magnetic inductor material (thereby reducing cost).These embodiments may drastically reduce the overall AC filter size andcost, and can provide a filtered AC output quality suitable for thegrid.

According to one aspect, a power electronics system is provided thatincludes a first inverter configured to receive direct current (DC)power from a power source, a second inverter configured to receive DCpower from the power source, a first output inductor connected in seriesto an alternating current (AC) output of the first inverter, a secondoutput inductor connected in series to an AC output of the secondinverter, a coupling inductor configured to receive current from thefirst output inductor and the second output inductor, and an AC poweroutput to provide current from the coupling inductor.

Some embodiments also include a control system configured to provide acontrol signal associated with a disturbance frequency, determine anamplitude of oscillation in an output power of the AC power output,wherein the oscillation is caused by the disturbance frequency, detectan islanding condition, if the amplitude of oscillation is below athreshold, and disconnect the grid from the AC power output if theislanding condition is detected.

In some embodiments, the coupling inductor includes a coil windingaround a coupled core and a self-inductance core. In furtherembodiments, the coil winding includes a series of elongated turns.

According to another aspect, power electronics system is provided thatincludes a first multi-phase inverter configured to receive directcurrent (DC) power from a power source, a second multi-phase inverterconfigured to receive DC power from the power source, a first pluralityof output inductors, each of the first plurality of output inductorsconnected in series to an output phase of the first multi-phaseinverter, a second plurality of output inductors, each of the secondplurality of output inductors connected in series to an output phase ofthe second multi-phase inverter, a plurality of coupling inductors, eachof the plurality of coupling inductors configured to receive currentfrom a respective output inductor of the first plurality of outputinductors and a respective output inductor of the second plurality ofoutput inductors, and a multi-phase alternating current (AC) poweroutput to provide current from the plurality of coupling inductors.

Some embodiments also include a control system configured to provide acontrol signal associated with a disturbance frequency, determine anamplitude of oscillation in an output power of the AC power output,wherein the oscillation is caused by the disturbance frequency, detectan islanding condition, if the amplitude of oscillation is below athreshold, and disconnect the grid from the AC power output if theislanding condition is detected.

In some embodiments, the coupling inductor includes a coil windingaround a coupled core and a self-inductance core. In furtherembodiments, the coil winding includes a series of elongated turns.

According another aspect, an inductor coil winding is provided thatincludes a first terminal, a series of concentric turns in a firstplane, the series of concentric turns leading in from the first terminaland having a diameter allowing for an opening within the series ofconcentric turns, a series of elongated turns in a second plane, theseries of elongated turns leading in from the series of concentric turnsand having a length greater than the diameter of the series ofconcentric turns, and allowing for an opening within the series ofelongated turns, and a second terminal, the second terminal leading outform the series of elongated turns.

According to some embodiments, the series of concentric turns providesmain inductance.

According to some embodiments, the series of elongated turns providescoupled inductance.

According to some embodiments, the first terminal is an input terminalelectrically connected to an output of an inverter to receive currentfrom the inverter.

Some embodiments also include a self-inductance core in the openingwithin the series of concentric turns and a coupled core in the openingwithin the series of elongated turns, the coupled core configured toprovide a magnetic coupling to another inductor coil winding.

According to another aspect, a filter assembly is provided that includesa first self-inductance core, a second self-inductance core, a couplercore, a first plurality of inductor coil windings, each of the firstplurality of inductor coil windings having a series of first turnsaround the first self-inductance core, and a series of second turnsaround the first self-inductance core and the coupler core, and a secondplurality of inductor coil windings, each of the second plurality ofinductor coil windings having a series of first turns around the secondself-inductance core, and a series of second turns around the secondself-inductance core and the coupler core.

In certain embodiments, the first self-inductance core, the secondself-inductance core, and the coupler core each include three limbs, onelimb for each of three phases. In some embodiments, the first turns ofeach of the first plurality of inductor coil windings are concentricturns and the first turns of each of the second plurality of inductorcoil windings are concentric turns.

In some embodiments, the second turns of each of the first plurality ofinductor coil windings are elongated turns and the second turns of eachof the second plurality of inductor coil windings are elongated turns.

According to certain embodiments, the first plurality of inductor coilwindings is configured to electrically connect to a first inverter at afirst terminal to receive an alternating current output from the firstinverter and the second plurality of inductor coil windings isconfigured to electrically connect to a second inverter at a secondterminal to receive an alternating current output from the secondinverter.

In some further embodiments, the first plurality of inductor coilwindings is electrically connected to the second plurality of inductorcoil windings at a third terminal configured to provide a combinedalternating current from the first and second inverter.

Certain embodiments also include a plurality of thermal platesinterspersed among the first and second plurality of inductor coilwindings and configured to remove thermal energy from the first andsecond plurality of inductor coil windings.

In various embodiments in accordance with principles of the presentinvention, a power electronics system comprises a first inverterconfigured to receive DC power from a power source, a second inverterconfigured to receive DC power from the power source, a first outputinductor connected in series to an output of the first inverter, asecond output inductor connected in series to an output of the secondinverter, a coupling inductor configured to receive current from thefirst output inductor and the second output inductor; and an AC poweroutput.

In other embodiments consistent with principles of the invention, apower electronics system comprises a first multi-phase inverterconfigured to receive DC power from a power source, a second multi-phaseinverter configured to receive DC power from the power source, a firstplurality of output inductors, each output inductor connected in seriesto an output phase of the first multi-phase inverter, a second pluralityof output inductors, each output inductor connected in series to anoutput phase of the second multi-phase inverter, a plurality of couplinginductors configured to receive current from an output inductor of thefirst plurality of output inductors and a output inductor of the secondplurality of output inductors having a corresponding phase, and amulti-phase AC power output.

Other embodiments of the power electronic systems further comprise acontrol system configured to provide a control signal associated with adisturbance frequency, determine an amplitude of oscillation in anoutput power of the AC power output, wherein the oscillation is causedby the disturbance frequency, detect an islanding condition, if theamplitude of oscillation is below a threshold, and disconnect the gridfrom the AC power output if the islanding condition is detected.

In accordance with principles of the invention, an inductor coil windingcomprises an input with a series of concentric turns in a first plane,the concentric turns having a diameter allowing for an opening withinthe series of concentric turns that provide main inductance to a filtersystem. The concentric turns lead into a series of elongated turns in asecond plane, the series of elongated turns leading in from the seriesof concentric turns and having a length greater than the diameter of theconcentric turns of the series of concentric turns, and allowing for anopening within the series of elongated turns. The opening within theseries of elongated turns being larger than the opening of the withinthe series of concentric turns to accommodate for a shared inductance.The series of elongated turns leads to an output of the inductor coil.

Other embodiments of the present invention provide a filter assemblycomprising a first self-inductance core, a second self-inductance core,and a coupler core. The embodiments further comprise a first pluralityof inductor coil windings, each inductor coil winding having an inputleading to a series of concentric turns in a first plane, the concentricturns having a diameter allowing for an opening within the series ofconcentric turns. The concentric turns lead to a series of elongatedturns in a second plane, the series of elongated turns leading in fromthe series of concentric turns and having a length greater than thediameter of the concentric turns of the series of concentric turns, andallowing for an opening within the series of elongated turns an output.The first plurality of inductor coil windings are arranged such that theopening within the series of concentric turns of the inductor coilwindings accommodate the first self-inductance core, and the openingwithin the series of elongated turns of the inductor coil windingsaccommodate the first self-inductance core and the coupler core. Asecond group of similar inductor coils are arranged such that theopening within the series of concentric turns of the inductor coilwindings accommodate the second self-inductance core, and the openingwithin the series of elongated turns of the inductor coil windingsaccommodate the second self-inductance core and the coupler core. Inembodiments consistent with principles of the present invention,self-inductance cores and a coupled core of a filter assembly may beprovided for three phases in a fully integrated implementation.

Still other aspects, examples, and advantages are discussed in detailbelow. Embodiments disclosed herein may be combined with otherembodiments in any manner consistent with at least one of the principlesdisclosed herein, and references to “an embodiment,” “some embodiments,”“an alternate embodiment,” “various embodiments,” “one embodiment” orthe like are not necessarily mutually exclusive and are intended toindicate that a particular feature, structure, or characteristicdescribed may be included in at least one embodiment. The appearances ofsuch terms herein are not necessarily all referring to the sameembodiment. Various aspects and embodiments described herein may includemeans for performing any of the described methods or functions.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one example are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and examples, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. In the figures,identical or nearly identical components illustrated in various figuresmay be represented by like numerals. For purposes of clarity, not everycomponent may be labeled in every figure. In the figures:

FIG. 1 is a schematic diagram of single phase power conversion bridgewith an AC filter;

FIG. 2 is a schematic diagram of two three-phase power bridges connectedin parallel employing output AC filters;

FIG. 3 is a schematic diagram of two single phase power conversionbridges coupled via a coupling inductor with a shared output AC filter;

FIG. 4 is a schematic diagram of two single phase power conversionbridges, with each bridge having an output AC filter, connected inparallel and coupled via a coupling inductor in accordance withprinciples of the invention;

FIG. 5 is a schematic diagram of two three phase power conversionbridges, with each phase of each bridge having an output AC filter,connected in parallel with each phase coupled via coupling inductors inaccordance with principles of the invention;

FIG. 6 is a perspective view of an example inductor coil in accordancewith principles of the invention;

FIG. 7 is a perspective view of an example filter assembly for a singlephase output of an inverter pair with connections to each inverterbridge in accordance with principles of the invention;

FIG. 8 is a perspective view of an example 3-phase inductor assembly inaccordance with principles of the invention;

FIG. 9 is a top view of the example 3-phase inductor assembly of FIG. 8;

FIG. 10 is a perspective view of the example 3-phase inductor assemblyof FIG. 8 including example integrated cooling components; and

FIG. 11 is a perspective view of the example cooling components of FIG.10, apart from the example 3-phase inductor assembly.

DETAILED DESCRIPTION

Aspects and embodiments provide inductor arrangements to couple two ormore inverters in parallel, in an extremely compact configuration, withefficient use of magnetic inductor material (thereby reducing cost).Embodiments in accordance with principles of the invention candrastically reduce the overall AC filter size and cost, and can providea filtered AC output quality suitable for the grid. A cooling system maybe mechanically integrated into the compact AC filter module for thermalmanagement in some embodiments.

It is to be appreciated that examples of the methods, systems, andapparatuses discussed herein are not limited in application to thedetails of construction and the arrangement of components set forth inthe following description or illustrated in the accompanying drawings.The methods, systems, and apparatuses are capable of implementation inother examples and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. Examplesdisclosed herein may be combined with other examples in any mannerconsistent with at least one of the principles disclosed herein, andreferences to “an example,” “some examples,” “an alternate example,”“various examples,” “one example” or the like are not necessarilymutually exclusive and are intended to indicate that a particularfeature, structure, or characteristic described may be included in atleast one example. The appearances of such terms herein are notnecessarily all referring to the same example. Also, the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting. The use herein of “including,” “comprising,”“having,” “containing,” “involving,” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items. References to “or” may be construed as inclusive sothat any terms described using “or” may indicate any of a single, morethan one, and all of the described terms. Any references to front andback, left and right, top and bottom, upper and lower, and vertical andhorizontal are intended for convenience of description, not to limit thepresent systems and methods or their components to any one positional orspatial orientation.

In an embodiment according to principles of the present invention, FIG.4 illustrates an example of two single-phase inverters 410, 420 (bridge1 and bridge 2) connected in parallel, each inverter 410, 420 having acorresponding output inductor 412, 422 (L1 and L2), respectivelyproviding self-inductance. The outputs are then magnetically coupled viaa coupled inductor 430 (L_(coupled)). With this arrangement, there ishalf as much current passing through each of inductors L1 and L2, asthere would be passing through L_(filter) in the conventional filterarrangement of FIG. 3. Thus in the arrangement of FIG. 4 losses may beapproximately halved relative to FIG. 3, for the same overall outputcurrent, reducing the amount of heat generated and providing moreefficient power conversion.

In other embodiments according to principles of the present invention,FIG. 5 shows a solar inverter system 500 of similar arrangement to FIG.4, but for two 3-phase inverters 510, 520 (bridges) connected inparallel. Corresponding phases (A, B, C) from each of the inverters 510,520 are coupled via a coupled inductor 530. In some embodiments, theinverters 510, 520 of solar inverter system 500 may be DC-to-ACinverters (or “power conversion bridges”), each rated for up to 1 MW (as2 MW of power cannot be handled by a single inverter). Each inverterproduces a 3-phase output. The two bridges are connected in parallel andthe 3-phase outputs of the 2 bridges are interleaved (180° out of phaserelative to each other). The inverters 510, 520 on their own may producean unacceptably rough AC power waveform. Therefore, an AC filter module540, consisting of inductor and capacitor components, is used to smooththe waveform.

To handle the level of power and power quality requirements, an ACfilter would conventionally be large and costly. For example, aclassical approach to this problem, even after much optimization,requires inductors that cost approximately 9% of the system cost andcapacitors that are approximately 2% of the system cost. The inductorused in the classical approach also produces significant energy losses(around 4 kW), which inflates the required cooling system and addsadditional cost and volume to the system.

As mentioned above, switching of the two 3-phase inverters 510, 520 inthe example system 500 may be interleaved, thereby doubling theswitching frequency. This essentially doubles the frequency seen by theinductors and therefore the amount of filtering required is reduced. Invarious embodiments, for each of the two inverters 510, 520, there is acore for each AC phase that provides self-inductance 550. For each ACphase, there is also a third core that provides a coupled inductance 530between the inverters 510, 520 (for each phase). Each of theself-inductors 550 is positioned between each inverter 510, 520 and therespective coupled inductor 530, per phase. The AC filter module 540thereby includes coupling between inverters and in some implementationsalso includes coupling between phases.

As discussed above, a solar inverter system may comprise two 3-phaseinverters connected in parallel, but a similar approach consistent withprinciples of the invention can be taken with more than two 3-phaseinverters and/or with two or more single phase or other multi-phaseinverters.

The above-described electrical configurations can be implemented in manydifferent embodiments, not limited to those described in further detailbelow.

In embodiments according to principles of the invention, the mechanicaldesign of an AC filter module has multiple novel aspects that allow thetechnology to be practically and commercially realized. Overall thecoupled inductor is ⅓ the total mass and ½ the volume of the classicalinductors when designed for equivalent losses. This results in a costreduction of the inductor components. Additional reductions in systemcost can be obtained through mechanical integration of cooling,structural features, and size reduction.

In conventional inductor systems, the coils or windings are wrappedaround a central core (often a straight cylindrical rod or a continuousloop or ring, doughnut). Embodiments of the present invention involve aunique winding geometry that is particularly suited for use inembodiments of an AC filter module. An example of such a winding isshown in FIG. 6.

The conductive material of an example winding 600 (e.g. copper oraluminum) may have a rectangular cross-section as shown. In variousembodiments, the conductive material may be one or more strands, and maybe multi-strand transpose wire in certain embodiments, e.g., to achieveadditional reduction in losses. The winding 600 is shaped to form aseries of concentric turns 610 in a first plane for the main inductance,then transitions to a second plane (parallel to the first) and is formedin to a series of concentric elongated turns 620. The circular opening612 accommodates a self-inductor core and the elongated opening 622accommodates a coupled inductor core. The coupled inductor turns 620also contribute to the self-inductance. In certain embodiments, thewinding 600 may be generally coated in an electrically insulatingmaterial, such as a plastic, except for the terminals 630.

Various embodiments of winding geometry, with respect to the exampleillustrated in FIG. 6, offer particular advantages. They are designed tointegrate the self and coupled inductor cores, and are designed to stackin a space-efficient manner, with the main inductance turns of onewinding in the same plane as the coupled inductance turns of an adjacentwinding. The stacks of windings can also be packed together tightlyside-by-side because of their quasi-rectangular shape. The flat/planarstructure of the windings also allows good thermal contact with thermalplates, such as liquid-cooled thermal plates, which can be interposedbetween stacked windings, for cooling the assembly (as described in moredetail below). Input and output terminals can be conveniently located atalmost any desired location around the perimeter of the winding. Inconventional windings, one terminal is often located inside the windingwhere it is less accessible.

Variations on the above winding geometry or quite different windinggeometries can be used in various implementations of the presentinvention. For example, in some variations on the above windinggeometry, the cross-section of the winding may be non-rectangular. Thenumber of turns for the main inductance and the coupled inductance canbe varied. The shape of the windings need not be as shown. The variouswinding turns need not be in two planes as shown, e.g., they may be in asingle plane or in multiple planes. In other winding geometries, thewinding turns may not have a planar-like configuration like the windingof FIG. 6. They may, for example, have a helical structure or a moreconventional geometry etc.

FIG. 7 shows an example AC filter assembly 700 for single-phase outputof an inverter pair with connections to each inverter bridge. Theassembly comprises 16 windings similar to those shown in FIG. 6 (withcircular openings to accommodate the cores), stacked in two side-by-sidestacks of 8. Self-inductance turns of the 8 windings connected to bridge1 are wound around self-inductance core 710. Similarly, self-inductanceturns of the 8 windings connected to bridge 2 are wound aroundself-inductance core 720. The coupled inductor turns of all 16 windingsare wound around the coupler core 730.

The physically interleaved windings stacked on each core are positionedto cancel what could otherwise be massive losses in the coupler core.There are multiple windings in parallel surrounding the various cores,which tends to reduce or minimize current crowding that can occur due toproximity of the windings to the magnetic material (cores) and otherconductors (windings).

For a pair of inverters with 3-phase (interleaved) output, threeseparate mechanical assemblies like that shown in FIG. 7 may be used. Incertain embodiments, however, the windings and inductors for all threephases of two or more inverters may be integrated into a single, compactassembly. An example of such an assembly is illustrated in perspectiveview in FIG. 8. A top view of the same example assembly is illustratedin FIG. 9.

In the example of FIG. 8, the 1st and 5th limbs of each core areoptional, depending on application, and/or the yoke of one or more ofthe cores may be removed, e.g., in an air core design. For example, ayokeless design for the self-inductor cores is enabled due to the corematerial magnetic properties and the arrangement of the cores. Such canreduce the core material mass and cost significantly.

The self-inductor cores and coupler cores can be made of any suitablemagnetic material. In some embodiments the self-inductor cores arepowdered iron or powdered iron alloys, and the coupler cores are pillarsor rods made of an amorphous material, with the perimeter constructedfrom Cold Rolled Grain Oriented laminated steel. Such a composition andconstruction can improve power losses and dissipation in the magneticmaterial.

FIG. 10 shows an example AC filter module for a pair of interleaved3-phase inverters comprising the assembly of FIG. 8 integrated with aliquid cooling system rack (shown individually in FIG. 11 below). Forexample, aluminum thermal plates with internal flow channels may beinterposed between the phase A/phase B windings and between the phaseB/phase C windings, and above the phase A windings and below the phase Cwindings. Liquid coolant supplied via a main coolant inlet manifold andcoolant lines, may be circulated through the plates, in parallel, tocool the electrical and magnetic components, and then directed viacorresponding outlet lines and an outlet manifold to an air-cooled heatexchanger. A pair of solid aluminum heat spreader plates may be includedto help dissipate heat generated deep inside the module, near thecoupler core, for example.

As mentioned above, in the assemblies shown in FIGS. 8-10, windings aretightly packed close together, reducing the size of the cores and theamount of magnetic material that is needed, and thereby reducing losses.Magnetic material in the pairs of phases may be shared in someembodiments. Embodiments of an inductor assembly, such as the exampleassembly shown in FIGS. 8-10, including a compact arrangement ofinductor windings for three phases (e.g., as compared to three separateassemblies like that assembly shown in FIG. 7), may provide improvedcompensation and cancellation of noise between coils of the assembly.

In some embodiments, an assembly or module as shown in FIGS. 8-10 may bepotted, e.g., in high temperature, thermally conductive, electricallyinsulating material. FIG. 11 illustrates the example cooling systemcomponents of the module shown in FIG. 10. The example cooling systemincludes liquid coolant that is distributed through coolant lines tovarious thermal plates to remove heat generated from the inductor coilsand electrical components.

Embodiments of the present invention provide a number of advantages,including the reduction of an AC filter size and cost, through use of acompact configuration, with efficient use of magnetic inductor andconductor materials. Examples and embodiments of AC filter/inductorassemblies described herein have the effect of providing an increasedpower density. In addition, they may provide reduced losses due to lowercurrent from the self-inductors being “upstream” of the coupledinductor, and reduced losses due to the interleaved physical arrangementof the windings on the coupler cores. The reduced losses result in lessheat generation, and reduced requirement for cooling. The design of thecores and windings provide for simple assembly, supporting manufacturingfeasibility. Further, the design allows for the use of liquid cooling ofa filter/inductor, which is generally more cost-efficient thanair-cooling, and allows for greater control or optimization of thedegree of thermal transfer.

In various embodiments, windings, arrangements, assemblies, and modulesin accord with aspects of those illustrated in FIGS. 4-10 may bebeneficially applied to provide electrical filtering to any of numerouspower converter applications, including those of solar inverters asdescribed herein, but also of DC-to-DC converters, AC-to-DC converters,and other DC-to-AC converters for applications other than solar. Sucharrangements may provide compact and efficient filtering to remove highfrequency components from an electrical waveform at inputs and/oroutputs of various power converters. Such arrangements may also bebeneficially adapted to differing scale of power conversion equipmentthan those discussed herein. For example, power factor correction (PFC)equipment, uninterruptible power supply (UPS) equipment, and the like.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the spirit and scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only, and the scope of the invention should be determinedfrom proper construction of the appended claims, and their equivalents.

What is claimed is:
 1. A power electronics system, comprising: a firstinverter configured to receive direct current (DC) power from a powersource; a second inverter configured to receive DC power from the powersource; a first output inductor connected in series to an alternatingcurrent (AC) output of the first inverter; a second output inductorconnected in series to an AC output of the second inverter; a couplinginductor configured to receive current from the first output inductorand the second output inductor; and an AC power output to providecurrent from the coupling inductor.
 2. The power electronics system ofclaim 1 further comprising a control system configured to provide acontrol signal associated with a disturbance frequency, determine anamplitude of oscillation in an output power of the AC power output,wherein the oscillation is caused by the disturbance frequency, detectan islanding condition, if the amplitude of oscillation is below athreshold, and disconnect the grid from the AC power output if theislanding condition is detected.
 3. The power electronics system ofclaim 1 wherein the coupling inductor includes a coil winding around acoupled core and a self-inductance core.
 4. The power electronic systemof claim 3 wherein the coil winding includes a series of elongatedturns.
 5. A power electronics system, comprising: a first multi-phaseinverter configured to receive direct current (DC) power from a powersource; a second multi-phase inverter configured to receive DC powerfrom the power source; a first plurality of output inductors, each ofthe first plurality of output inductors connected in series to an outputphase of the first multi-phase inverter; a second plurality of outputinductors, each of the second plurality of output inductors connected inseries to an output phase of the second multi-phase inverter; aplurality of coupling inductors, each of the plurality of couplinginductors configured to receive current from a respective outputinductor of the first plurality of output inductors and a respectiveoutput inductor of the second plurality of output inductors; and amulti-phase alternating current (AC) power output to provide currentfrom the plurality of coupling inductors.
 6. The power electronicssystem of claim 5 further comprising a control system configured toprovide a control signal associated with a disturbance frequency,determine an amplitude of oscillation in an output power of the AC poweroutput, wherein the oscillation is caused by the disturbance frequency,detect an islanding condition, if the amplitude of oscillation is belowa threshold, and disconnect the grid from the AC power output if theislanding condition is detected.
 7. The power electronics system ofclaim 5 wherein each of the plurality of coupling inductors includes acoil winding around a coupled core and a self-inductance core.
 8. Thepower electronic system of claim 7 wherein the coil winding includes aseries of elongated turns.
 9. An inductor coil winding comprising: afirst terminal; a series of concentric turns in a first plane, theseries of concentric turns leading in from the first terminal and havinga diameter allowing for an opening within the series of concentricturns; a series of elongated turns in a second plane, the series ofelongated turns leading in from the series of concentric turns andhaving a length greater than the diameter of the series of concentricturns, and allowing for an opening within the series of elongated turns;and a second terminal, the second terminal leading out form the seriesof elongated turns.
 10. The inductor coil winding of claim 9 wherein theseries of concentric turns provides main inductance.
 11. The inductorcoil winding of claim 10 wherein the series of elongated turns providescoupled inductance.
 12. The inductor coil winding of claim 11 whereinthe first terminal is an input terminal electrically connected to anoutput of an inverter to receive current from the inverter.
 13. Theinductor coil winding of claim 9 further comprising a self-inductancecore in the opening within the series of concentric turns and a coupledcore in the opening within the series of elongated turns, the coupledcore configured to provide a magnetic coupling to another inductor coilwinding.
 14. A filter assembly comprising: a first self-inductance core;a second self-inductance core; a coupler core; a first plurality ofinductor coil windings, each of the first plurality of inductor coilwindings having a series of first turns around the first self-inductancecore, and a series of second turns around the first self-inductance coreand the coupler core; and a second plurality of inductor coil windings,each of the second plurality of inductor coil windings having a seriesof first turns around the second self-inductance core, and a series ofsecond turns around the second self-inductance core and the couplercore.
 15. The filter assembly of claim 14 wherein the firstself-inductance core, the second self-inductance core, and the couplercore each include three limbs, one limb for each of three phases. 16.The filter assembly of claim 14 wherein the first turns of each of thefirst plurality of inductor coil windings are concentric turns and thefirst turns of each of the second plurality of inductor coil windingsare concentric turns.
 17. The filter assembly of claim 16 wherein thesecond turns of each of the first plurality of inductor coil windingsare elongated turns and the second turns of each of the second pluralityof inductor coil windings are elongated turns.
 18. The filter assemblyof claim 14 wherein the first plurality of inductor coil windings isconfigured to electrically connect to a first inverter at a firstterminal to receive an alternating current output from the firstinverter and the second plurality of inductor coil windings isconfigured to electrically connect to a second inverter at a secondterminal to receive an alternating current output from the secondinverter.
 19. The filter assembly of claim 18 wherein the firstplurality of inductor coil windings is electrically connected to thesecond plurality of inductor coil windings at a third terminalconfigured to provide a combined alternating current from the first andsecond inverter.
 20. The filter assembly of claim 14 further comprisinga plurality of thermal plates interspersed among the first and secondplurality of inductor coil windings and configured to remove thermalenergy from the first and second plurality of inductor coil windings.